dial with P and SG keys for
P = Priority
SG = Special Grade
Buttons were typically assigned as follows:
4-wire line 1
4-wire line 2
Auxiliary Transfer Key
There is also an exclusion key under the left plunger.
|Note the key
profile. The spherical
detent in the middle of each button is smaller than the
The designation strip covers are beveled and held in place with pins, like those on the earlier 400-series keysets and late 1950s vintage prototype sets. The pins go into a metal plate that the dial pad is mounted on -- a much more expensive arrangement than that used by later keysets and TouchTone pads.
shows the 4-wire relay (above the
ringer coil) and additional terminal strip.
The relay disconnects the receiver from the network. A repeating coil matches the receiver to the receiving loop, to obtain a 4-wire termination.
|Back view of
the 22A TouchTone pad.
Each button push produces two tones.
BSP C38.595.06, Issue 1, June 1961 identifies the frequencies generated as:
Columns: 1209, 1336 and 1477 cps
Rows: 697, 770, 852 and 941 cps.
(Standard TouchTone frequencies.)
The BSP specifies set availability in black only.